Note: Descriptions are shown in the official language in which they were submitted.
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FERROMAGNETIC BULLET
This invention relates generally to projectiles
and more particularly to a lead free, ferromagnetic
projectile.
Lead pro3ectiles and lead shot expended at
shooting ranges pose a significant environmental
hazard. Disposal of the lead cont~r;n~ted sand used
as a backstop in indoor ranges is expensive, since
lead is a hazardous material. Due to the low value
of lead metal, reclamation of the lead from the sand
is not economically feasible for most target ranges.
At outdoor ranges, the lead must be removed before
the range land can be used for other purposes.
Frequently, the entire top soil layer is removed and
disposed elsewhere, a time consuming and costly
operation.
Accordingly, there exists a need for an
effective lead free bullet that is easily separated
from range soil and sand.
Density differences between bullets of the same
size result in differences in long range trajectory
and differences in firearm recoil. Such differences
are undesirable. The shooter needs to have a
consistent trajectory and a recoil so the "feel" of
shooting a lead free practice round should be
similar to that of shooting a lead service round. If
there are diff~erences in trajectory and recoil,
experience gained on the practice range will
degrade, rather than improve, accuracy when firing a
lead bullet in the field.
Various approaches have been used to produce
shot pellets that are non toxic. U.S. Patent Nos.
4,027,594 and 4,428,295 assigned to the assignee of
the present invention, disclose pellets made of one
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or more metal powders where one of the powders is
lead.
U.S. Patent Nos. 2,995,090 and 3,193,003
disclose frangible gallery bullets made of iron
powder, a small amount of lead powder, and a
thermoset resin. While substantially lead free, a
drawback of these bullets is a density significantly
less than that of a lead bullet.
U.S. Patent No. 4,881,465 discloses a shot
pellet made of lead and ferrotungsten, while U.S.
Patent Nos. 4,850,278 and 4,939,996 disclose a
projectile made of ceramic zirconium. U.S. Patent
No. 4,005,660 discloses a polyethylene matrix which
is filled with a metal powder such as bismuth,
tantalum, nickel, and copper. Yet another frangible
projectile is made of a polymeric material which is
filled with metal or metal oxide.
U.S. Patent No. 4,949,644 discloses shot made
of bismuth or a bismuth alloy. However, bismuth is
in short supply and considerably more expensive than
lead.
U.S. Patent No. 5,088,415 discloses a plastic
covered lead shot. However, this shot material
still contains lead, which upon backstop impact,
will be exposed to the environment. Plated lead
bullets and plastic coated lead bullets are also in
use, but they have the same drawback, on target
impact the lead is exposed creating difficulty in
disposing of spent bullets.
None of the prior bullets noted above has
proved commercially viable, either due to cost,
density differences, difficulty of mass production
or difficulty of disposal. Accordingly, there
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- remains a need for a projectile for target shooting
ranges or for hunting use which is substantially
lead free, performs ballistically similar to lead
and facilitates reclamation of target backstops and
range soil.
Accordingly, it is an object of the invention
to provide a projectile that is substantially lead
free. A second object of the invention is for the
projectile to have ballistic performance similar to
lead. A third object of the invention is for the
projectile to be easily removed from the shooting
range soils and backstops.
It is a feature of the invention that the
projectile is a sintered composite having one or
more, high density constituents selected from the
group consisting of tungsten carbide, tungsten,
ferrotungsten, cemented tungsten carbide alloys and
carboloy (a tungsten carbide-cobalt sintered alloy,
typically cont~;n;ng from 3% to 13% by weight
cobalt), and a second, lower density constituent
selected to be a metallic matrix material such as
tin, zinc, iron, nickel, cobalt and copper.
Alternatively, the second constituent is a plastic
matrix material such as a phenolic, epoxy,
dialylphthalate, acrylic, polystyrene, polyethylene,
or polyurethane. It is another feature of the
invention that an effective amount, typically more
than 50% by weight, of the projectile constituents
are ferromagnetic. In addition, the composite
projectile may contain a filler metal such as iron
powder or zinc powder. The bullet of the invention
comprises a solid body having a density of at least
about 9 grams per cubic centimeter (80 percent that
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of pure lead) and a yield strength in compression
greater than about 31 MPa (4500 psi).
Other constituents may be added in small
amounts for special purposes such as enhancing
frangibility. If iron is one constituent, the
addition of carbon results in a brittle
microstructure after a suitable heat treatment.
Lubricants or solvents can be added to enhance
powder flow properties, compaction properties and
ease die release.
It is an advantage of the invention that
ferrotungsten is ferromagnetic and has a density
greater than that of lead. A ferrotungsten
containing composite is economically feasible for
projectiles and, by metallurgical and ballistic
analysis, can be alloyed in proper amounts under
proper conditions to become useful for a lead free
bullet.
The invention further stems from the
realization that ballistic performance can best be
measured by actual shooting experiences since the
extremes of acceleration, pressure, temperature,
frictional forces, centrifugal acceleration and
deceleration forces, impact forces both axially and
laterally, and performance against barriers typical
of bullet stops in current usage impose an extremely
complex set of re~uirements on a bullet that make
accurate theoretical prediction virtually
impossible.
FIG. l is a bar graph of densities of powder
composites.
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FIG. 2 is a bar graph of the ~;~um
engineering stress attained under compression with
the powder composites.
FIG. 3 is a bar graph of the total energy
absorbed during compressive deformation to 20%
strain or fracture.
FIG. 4 is a bar graph showing the maximum
stress at 20% compressive deformation.
FIG. 5 is a bar graph showing the total energy
absorbed in 20% compressive deformation or fracture
of the bullets of FIG. 4.
There are at least six requirements for a
successful lead free bullet. First, the bullet must
closely approximate the recoil of a lead bullet when
fired so that the shooter feels as though he is
firing a standard lead bullet. Second, the bullet
must closely approximate the trajectory, i.e.
exterior ballistics, of a lead bullet of the same
caliber and weight so that the practice shooting is
directly relevant to shooting in the field with an
actual lead bullet. Third, the bullet must not
penetrate or damage the normal steel plate backstop
on the target range and must not ricochet
significantly. Fourth, the bullet must remain
intact during its travel through the gun barrel and
while in flight. Fifth, the bullet must not damage
the gun barrel. Sixth, the cost of the bullet must
be reasonably comparable to other alternatives.
In order to meet the first two requirements,
the lead free bullet must have approximately the
same density as lead. This means that the bullet
must have an overall density of at least 80% that of
lead or 9 grams per cubic centimeter.
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The third requirement, not penetrating or
damaging the steel backstops at target shooting
ranges, dictates that the bullet must either (l)
deform at stresses lower than that sufficient to
penetrate or severely damage the backstop, (2)
fracture into small pieces at low stresses or (3)
both deform and fracture at low stress.
As an example, a typical 158 grain lead (lO.3
gm, 0.0226 lb.) .38 Special bullet has a muzzle
kinetic energy from a lO.2 cm (4 inch) barrel of 272
joules (200 foot pounds) and a density of ll.35
gm/cm3 (0.4l pounds per cubic inch). This
corresponds to an energy density of 296 joules/cm3
(43,600 inch pounds per cubic inch). The deformable
lead free bullet in accordance with the invention
must absorb enough of this energy per unit volume as
strain energy (elastic plus plastic) without
imposing on the backstop stresses higher than the
yield strength of mild steel, about 310 MPa (about
45,000 psi) in order for the bullet to stop without
penetrating or severely damaging the target
backstop. In the case of a frangible bullet or a
deformable frangible bullet, respectively, the
fracture stress of the bullet must be below the
stresses experienced by the bullet upon impact with
the target backstop and below the yield strength of
mild steel.
The requirements that the bullet remain intact
as it passes through the barrel and that the bullet
not cause excessive barrel erosion are more
difficult to quantify. Actual shooting tests are
normally required to ~etermine this quality.
However, if needed, the bullet of the invention may
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be coated with metal or plastic or jacketed in a
conventional m~nner to protect the barrel.
The requirement that the projectile be
reclaimable from shooting range environments such as
sand traps and top soil is best satisfied by
including in the projectile a ferromagnetic
constituent. Ferromagnetic materials are those
metals, alloys and compounds of the transition (iron
group), rare-earth and actinide elements that, below
the Curie temperature, have atomic magnet moments
tending to line up in a common direction. These
materials are characterized by a strong attraction
to other magnetized materials.
The weight percent of the ferromagnetic
component is at least that effective to impart the
sintered fragments of a spent projectile with
ferromagnetic capability. The particles are then
separated from the sand or other environment using
magnetic separation ~hn;~ues.
The reclaimed projectile fragments can be
further processed to separate the ferromagnetic
constituent from the projectile matrix and any
coating or jacket. For example, separation may
include ~Pch~nical crushing or grinding, or for
polymer matrix, burning or chemically dissolving the
matrix.
Suitable ferromagnetic constituents for the
high density first component include ferrotungsten
and cemented tungsten carbide alloys having a
ferromagnetic addition. Ferrotungsten is generally
understood to be a tungsten base alloy that includes
iron having a tungsten content by weight of from
about 70~ to about 85%. Preferably, the carbon
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content of the ferrotungsten is less than about
0.6%. In this patent application, any tungsten base
alloy cont~;n;ng iron that exhibits ferromagnetism
is included.
In the projectile, the ferrotungsten is present
in a weight percent above about 50% and preferably
from about 70% to 90% is preferred.
When the second constituent of the projectile
is to provide the ferromagnetism, suitable
ferromagnetic constituents for the lower density
second component include iron, nickel and cobalt.
Iron is most preferred due to its low cost.
Preferably, the iron is present in an amount of from
about 10% to about 30% by weight.
The metal matrix bullets in accordance with the
preferred embodiments of the present invention are
fabricated by powder metallurgical techniques. For
the more frangible materials, the powders of the
individual constituents are blended, compacted under
20 pressure to near net shape, and sintered. If the
bullets are jacketed, compacting and sintering can
be done in the jacket or the bullets could be
compacted and sintered before insertion into the
jackets. If the bullets are coated, they would be
25 coated after compacting and sintering.
The proportions of the several powders required
for a desired density is different than that
calculated by the rule of mixtures because of the
inability to eliminate all porosity. Porosity is
30 compensated for by an appropriate increase in the
amount of the higher density constituent, typically
tungsten, ferrotungsten, carboloy, tungsten carbide q
or mixtures thereof. The optimum mixture is
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determined by the tradeoff between raw material cost
and bullet performance.
For the more ductile matrix materials such as
the metals mentioned above, the bullets may be made
by the above process or alternatively, compacted
into rod or billet shapes using conventional
pressing or isostatic pressing techniques. After
sintering, the rod or billet could then be extruded
into wire for fabrication into bullets by forging
using punches and dies as is done with conventional
lead bullets. Alternatively, if the materials are
too brittle for such fabrication, conventional
fabrication processes could be used to finish the
bullet.
lS The frangibility of the composite bullet can be
enhanced through various processing steps. An
optional heat treatment to embrittle the matrix
enhances frangibility after final shape forming.
For example, an iron matrix bullet having a carbon
addition could be embrittled by suitable heat
treatment.
A tin matrix bullet could be embrittled by
controlled tempering at a temperature where partial
transformation to alpha tin occurs. Typically, this
temperature is from about 375OC to about 575C.
This method can provide precise control of the
degree of frangibility.
A third method to enhance embrittlement is by
selecting impurity additions such as bismuth in a
copper matrix composite. After fabrication, the
bullet may be heated to a temperature range where
the impurity collects preferentially at grain
boundaries.
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In addition, even without embrittling
additives, frangibility can be controlled by
suitably varying the sintering time and/or sintering
temperature.
s When the composite projectile has a
thermoplastic or thermosetting plastic matrix, the
metallic powders and polymer powders are blended as
described considering mass and density requirements.
The mixture is then formed into the final part by
any conventional process used in of polymer
technology such as injection molding, transfer
molding.
In the case of jacketed plastic matrix bullets,
compacting under heat can be done with the composite
powder inside the jacket. Alternatively, the
powders can be compacted using pressure and heat to
form pellets for use in such processes.
To protect the gun barrel from damage during
firing, the composite bullets of the invention are
preferably jacketed or coated with a soft metallic
or plastic coating. The coatings is preferably tin,
zinc, copper, brass or plastic. One suitable
ferromagnetic jacket material is iron.
For plastic matrix bullets, plastic coatings
are preferred. In a most preferred embodiment, the
plastic matrix and the coating are the same polymer.
Plastic coatings may be applied by dipping,
spraying, fluidized bed or other conventional
plastic coating processes. The metallic coatings
may be applied by electroplating, hot dipping or
other conventional coating processes.
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.
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The benefits of the composite bullets of the
invention will become more apparent from the
Examples that follow.
EXAMPLES
A. Plastic Matrix
Frangible plastic matrix composite bullets were
made of tungsten powder with an average particle
size of 6 microns. Iron powder was added to the
tungsten powder at levels of 0, 15, and 30 percent
by weight. After blending with one of two polymer
powders, phenyl formaldehyde (Lucite) or
polymethylmethalcrylate (Bakelite) which acted as
the matrix, the mixtures were hot compacted at a
temperature within the range of from about 149C to
about 177C (300F-350F) and a pressure of about
241 MPa - 276 MPa (35-40 ksi) into 3.18 cm (1.25
inch) diameter cylinders which were then cut into
rectangular parallelepipeds for compression testing
and drop weight testing.
In all, six (6) samples were made as shown in
Table I below:
TABLE I
SAMPLE # COMPOSITION
1 Lucite - Tungsten
2 Lucite - 85% Tungsten - 15% Iron
3 Lucite - 70% Tungsten - 30% Iron
4 Bakelite - Tungsten
Bakelite - 85% Tungsten - 15% Iron
6 Bakelite - 70% Tungsten - 30% Iron
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The bullet materials so formed were very
frangible in the compression test. Their behavior
in the drop weigh~ test was similarly highly
frangible. The densities relative to that of lead
for these samples ar shown in Table II below:
TABL~ II
SAMPLE DENSITY STRESS ENERGY
ABSORBED
1 81% 29.6MPa (4.3ksi) 0.34J/cm3
(49 in-lb/in3)
2 78% 23.4MPa (3.4ksi) 0.28J/cm3
(40 in-lb/in3)
3 75% 18.6MPa (2.7ksi) 0.15J/cm3
(21 in-lb/in3)
4 84% 32.4MPa (4.7ksi) 0.28J/cm3
(40 in-lb/in3)
80% 9.65MPa (1.4ksi) 0.069J/cm3
(10 in-lb/in3)
6 78% 13.lMPa (1.9ksi) 0.062J/cm3
(9 in-lb/in3)
The maximum stress in the compression test and
the energy absorbed in the compression test for
these materials is also recorded in Table II. The
m~;mum stress before fracture was below 34.5 MPa (5
ksi) which is well within the desired range to avoid
backstop damage.
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Metal Matrix Composites
Figure l shows the densities attained with
metal matrix composites made of tungsten powder,
tungsten carbide powder or ferrotungsten powder
blended with powder of either tin, bismuth, zinc,
iron (with 3~ carbon), aluminum, or copper. The
proportions were such that they would have the
density of lead if there was no porosity after
sintering. The powders were cold compacted into
12.7 mm (half-inch) diameter cylinders using
pressures of 690 MPa (lO0 ksi). They were then
sintered for two hours at appropriate temperatures,
having been sealed in stainless steel bags. The
sintering temperatures were (in degrees Celsius)
180, 251, 350, 900, 565, 900 respectively.
Figure 2 shows the mA~i ~ axial internal
stresses attained in the compression test. Figure 3
shows the energies absorbed up to 20 percent total
strain (except for the copper tungsten compact which
reached such high internal stresses that the test
was stopped before 20 percent strain was achieved).
All of the materials exhibited some plastic
deformation. The energy absorptions in the
compression test indicate the relative ductilities,
with the more energy absorbing materials being the
most ductile.
Even the most ductile samples such as the tin
and bismuth matrix composites showed some fracturing
during the compression test due to barreling and
secondary tensile stresses which result from this.
In the drop weight test using either 326 Joules (240
foot pounds) or 163 Joules (120 foot pounds), the
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behavior was similar to but an exaggeration of that
observed in the compression test.
Control Examples
Figure 4 shows, for comparison, a lead slug,
two standard 38 caliber bullets, and two commercial
plastic matrix composite bullets tested in
compression. Figure 4 shows that maximum stresses
of the lead slug and lead bullets were significantly
less than those of the plastic bullets. However,
all were of the same order as those attained by the
metal matrix samples in the iron free plastic matrix
samples. Figure 5 shows the energy absorption for
these materials. Values are generally less than
that of the metal matrix samples shown in Figure 3
and much higher than that of the frangible plastic
matrix samples.
All of these materials deformed significantly
in the 326 Joules (240 ft.-lb.) drop weight test.
The lead samples did not fracture, whereas the
plastic matrix bullets did.
~acketed Composite Bullets
As another example, 38 caliber metal-matrix
bullets and plastic-matrix bullets with the
compositions listed in Table I were fabricated
inside st~n~rd brass jackets (deep-drawn cups)
which had a wall thickness varying from 0.25 mm
(O.OlO inch) to 0.64 mm (0.025 inch). The
plastic-matrix ("Lucite" or "Bakelite" listed as
code l and code 2 in the Table) samples were
compacted at the temperature described in the first
example. The metal-matrix samples (Codes 3-ll) were
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compacted at room temperature and sintered as
described above while they were encased in the
jackets.
These bullets were fired into a box of sawdust
using a +P load of powder, exposing them to
pressures in excess of 138 MPa (20,000 pounds per
square inch) while in the barrel. ~ination and
weighing of the samples before and after firing
revealed that the iron-matrix, copper-matrix and
zinc-matrix bullets lost no weight and no material
~rom the end of the composite core that had been
exposed to the hot gases in the barrel.
Microstructural e~;n~tion revealed that only the
pure bismuth bullet had internal cracks after being
fired.
These bullets were also fired at a standard
steel plate backstop 5.1 mm (0.2 inch thick),
hardness of Brinell 327 at an incidence angle of 45
degrees and a distance typical of indoor pistol
ranges. None of the bullets damaged the backstop or
ricocheted.
While the invention has been described in terms
of frangible projectiles, the ferromagnetic
materials of the invention also can find utility in
articles used to direct an explosive charge such as
shaped charge liners and cones in oil well fields.
While the invention has been described with
reference to preferred embodiments and specific
examples, it is apparent that many changes,
modifications and variations can be made without
departing from the inventive concept disclosed
herein. Accordingly, the spirit and broad scope of
the appended claims is intended to embrace all such
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changes, modifications and variations that may occur
to one of skill in the art upon a reading of the
disclosure.
